Peracid compositions have been reported to be effective antimicrobial agents. Methods to clean, disinfect, and/or sanitize hard surfaces, meat products, living plant tissues, and medical devices against undesirable microbial growth have been described (e.g., U.S. Pat. Nos. 6,545,047; 6,183,807; 6,518,307; 5,683,724; and U.S. Patent Application Publication No. 2003/0026846). Peracids have also been reported to be useful in preparing bleaching compositions for laundry detergent applications (U.S. Pat. Nos. 3,974,082; 5,296,161; and 5,364,554).
Peracids can be prepared by the chemical reaction of a carboxylic acid and hydrogen peroxide (see Organic Peroxides, Daniel Swern, ed., Vol. 1, pp 313-516; Wiley Interscience, New York, 1971). The reaction is usually catalyzed by a strong inorganic acid, such as concentrated sulfuric acid. The reaction of hydrogen peroxide with a carboxylic acid is an equilibrium reaction, and the production of peracid is favored by the use of an excess concentration of peroxide and/or carboxylic acid, or by the removal of water.
Some peracid-based disinfectants or bleaching agents are comprised of an equilibrium mixture of peracid, hydrogen peroxide, and the corresponding carboxylic acid. One disadvantage of these commercial peracid cleaning systems is that the peracid is oftentimes unstable in solution over time. One way to overcome the stability problem is to generate the peracid prior to use by combining multiple reaction components that are individually stable for extended periods of time. Preferably, the individual reaction components are easy to store, relatively safe to handle, and capable of quickly producing an efficacious concentration of peracid upon mixing.
The CE-7 family of carbohydrate esterases has recently been reported to have perhydrolase activity. These “perhydrolase” enzymes have been demonstrated to be particularly effective for producing peracids from a variety of carboxylic acid ester substrates when combined with a source of peroxygen (See WO2007/070609 and U.S. Patent Application Publication Nos. 2008/0176299 and 2008/176783 to DiCosimo et al.; each herein incorporated by reference in their entireties). Some members of the CE-7 family of carbohydrate esterases have been demonstrated to have perhydrolytic activity sufficient to produce 4000-5000 ppm peracetic acid from acetyl esters of alcohols, diols, and glycerols in 1 minute and up to 9000 ppm between 5 minutes and 30 minutes once the reaction components were mixed (DiCosimo et al., U.S. Patent Application Publication No. 2009/0005590).
The enzymatic peracid generation system described by U.S. 2009/0005590 to DiCosimo et al. is typically based on the use of multiple reaction components that remain separated until the peracid solution is needed. Using this approach overcomes the peracid instability issues associated with storage of many peracid-based disinfectants and bleaching agents. However, specific formulations that provide long term stability of perhydrolase activity when using multicomponent formulations comprising CE-7 carbohydrate esterases remains to be addressed. Of particular concern is the long term storage stability of a CE-7 enzyme having perhydrolysis activity when stored in an organic liquid or solvent having a log P (i.e., the logarithm of the partition coefficient of a substance between octanol and water, where P equals [solute]octanol/[solute]water) of less than two. Several of the organic ester substrates previous described by DiCosimo et al. have log P values of less than two.
Organic liquids or solvents can be deleterious to the activity of enzymes, either when enzymes are suspended directly in organic liquids or solvents, or when miscible organic/aqueous single phase liquids or solvents are employed. Two literature publications that review the effects of organic solvents on enzyme activity and structure are: (a) C. Laane et al., Biotechnol. Bioeng. 30:81-87 (1987) and (b) Cowan, D. A. and Plant, A., Biocatalysis in Organic Phase Systems., Ch. 7 in Biocatalysis at Extreme Temperatures, Kelly, R. W. W. and Adams, M., eds., Amer. Chem. Soc. Symposium Series, Oxford University Press, New York, N.Y., pp 86-107 (1992). Cowan and Plant, supra, note (on page 87) that the art generally recognizes that there is little or no value in using organic solvents having a log P≦2 to stabilize intracellular enzymes in an organic phase system. Organic solvents having a log P between two and four can be used on a case-by-case basis dependent on enzyme stability, and those having a log P>4 are generally useful in organic phase systems.
Cowan and Plant, supra, further note (on page 91) that the effect of direct exposure of an enzyme dissolved in a single-phase organic-aqueous solvent depends on solvent concentration, solvent/enzyme surface group interactions, and solvent/enzyme hydration shell interactions. Because a solvent's log P value must be sufficiently low so that the solvent is fully miscible with the aqueous phase to produce a single-phase, a single-phase organic-aqueous solvent containing a low log P organic solvent usually has a negative effect on enzyme stability except in low organic solvent concentration applications. Triacetin is reported to have a log P of 0.25 (Y. M. Gunning, et al., J. Agric. Food Chem. 48:395-399 (2000)), similar to that of ethanol (log P −0.26) and isopropanol (log P 0.15) (Cowan and Plant); therefore the storage of enzyme powder in triacetin would be expected to result in unacceptable loss of enzyme activity, as would the use of additional cosolvents with log P<2 (e.g., cyclohexanone, log P=0.94) (Cowan and Plant); 1,2-propanediol, log P=−1.41 (Gunning, et al.); 1,3-propanediol, log P=−1.3 (S-J. Kuo, et al., J. Am. Oil Chem. Soc. 73:1427-1433 (1996); diethylene glycol butyl ether, log P=0.56 (N. Funasaki, et al., J. Phys. Chem. 88:5786-5790 (1984); triethyleneglycol, log P=−1.75 (L. Braeken, et al., Chem Phys Chem 6:1606-1612 (2005)).
Thus, the problem to be solved is to formulate a product using a mixture of a peracid-generating enzyme in an organic ester substrate employed for peracid production, where the enzyme retains significant perhydrolase activity even when stored in a mixture with the carboxylic acid ester substrate.